2004 Mercury 115 ELPTO surging

A

aidanmurphy

Petty Officer 2nd Class
Joined
Apr 2, 2022
Messages
113
Hey everyone, picked up a new to me 2003 Key Largo 180cc. Super clean boat and came with the 115 2 stroke Mercury.

The motor idles perfectly and has great holeshot and does not bog down at all.

However, upon pushing at higher RPM, the boat feels like it is surging or will not hold high RPM. It will cruise well, but there is still the occasional surge that is almost imperceivable. However when pushing for the last 1/4th of throttle the boat just falls back down.

Previous owner said he cleaned the carbs, replaced the fuel pump. I checked the fuel pickup and the fuel filter and both are clean. I stuck a scope in the pickup into the tank and it doesn't look spotless but it doesn't look terrible either. Anywhere I should be looking in particular?

The tachometer also does not work.
 
Last edited:
M

Mc Tool

Petty Officer 1st Class
Joined
Aug 7, 2024
Messages
312
Sure does sound like a fuel flow issue .
Get the carbs primed up and remove fuel feed hose from carbs and direct at a suitable container , start engine and confirm that fuel is being delivered at a reasonable pressure ( put finger over end of hose and try and make it spray a bit ). The longer you can continue this test the better as the fuel may flow well initially and them taper off . .
If someone has had the carbs apart ( like the PO ) you pretty much gotta make sure he hasnt cocked it up , like float levels
When you say "falls back down " do you mean all cylinders start failing , or does it start loosing only a couple of cylinders ?
The fact that its ok at 3/4 throttle but not full *** does sound like feul BUT dont get tunnel vision .
If you have another fuel hose , from tank to motor, try that .
 
A

aidanmurphy

Petty Officer 2nd Class
Joined
Apr 2, 2022
Messages
113
Thanks for the response. I was thinking the same thing.. If PO says he went through the carbs I better make sure it was done correctly.

When I mean "falling off" I mean the boat will get to say 4500RPM and then drop back down to 4000RPM, even if you keep adding throttle. I agree it does sound fuel related, but I have new spark plugs and wires coming just to cross off some intermittent spark issues. The boat idles great, will never shut off and has what feels like full power coming out of the hole. It is just the top end band mainly that it can't reach.

I will plan to do that carb trick and maybe take them off to check the work that was done.
 
R

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
38,411
Have an assistant operate the manual fuel pump during a test run.----Test run on another tank and hose.
 
R

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
38,411
Correct.-----The bulb is a simple manual pump.-----It can be a useful trouble shooting tool.-----The fuel pump on the motor is also easy to inspect / install a repair kit.-----Oil injection has been tested ?----You have installed a new water pump impeller when you got the boat ?
 
A

aidanmurphy

Petty Officer 2nd Class
Joined
Apr 2, 2022
Messages
113
racerone said:
Correct.-----The bulb is a simple manual pump.-----It can be a useful trouble shooting tool.-----The fuel pump on the motor is also easy to inspect / install a repair kit.-----Oil injection has been tested ?----You have installed a new water pump impeller when you got the boat ?
Click to expand...
PO installed new impeller, it pisses strong. PO also said he installed a new fuel pump. Visually it looks new, I can pull it apart if moving to a new aux fuel tank + new plugs and wires doesn't help anything. That is going to be my next step.

I have not directly tested oil injection but when I looked at the plugs they were a tad oily and didn't look leaned out.

What is the best way to directly test the oil injection?
 
A

aidanmurphy

Petty Officer 2nd Class
Joined
Apr 2, 2022
Messages
113
cyclops222 said:
A 2 stroke with oily plugs ?
Who mixed the oil ratio ?
Click to expand...
It's not premix, it is oil injected. I will be going through the system with the manual when it comes in and make sure the ratio is adjusted properly if that is something that is possible
 
Texasmark

Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,778
aidanmurphy said:
Do you mean having my wife squeeze the bulb while the surging behavior exists? Can do
Click to expand...
That will expose a lot of sins. Surging is fuel related and obviously RPMs fall off when fuel flow falls off. When the PO said he checked the onboard fuel filter (and there are 2 on that engine, a large one visible from the Port side of the engine with the cowling off and another much smaller one for cylinders 3 and 4 tucked in behind and at the rear of the oil tank.

Under 2500 RPMs 3 and 4 aren't used. Only used above. Your problem is above...........

I "unknowingly" question how the PO checked the large filter and "betcha" didn't know or didn't bother with the small one for 3 and 4........which uses the large one too since is has a small amount of fuel mix added to the cylinders for lubrication, but not enough at low RPMs for combustion.....
Getting access to the large filter or a fuel line down wind of it is a PIA and if you went through the trouble of getting it out so that you could blow through it you might as well change it......about 10 bucks. I just sold my 2002 115 2+2.
 
A

aidanmurphy

Petty Officer 2nd Class
Joined
Apr 2, 2022
Messages
113
Texasmark said:
That will expose a lot of sins. Surging is fuel related and obviously RPMs fall off when fuel flow falls off. When the PO said he checked the onboard fuel filter (and there are 2 on that engine, a large one visible from the Port side of the engine with the cowling off and another much smaller one for cylinders 3 and 4 tucked in behind and at the rear of the oil tank.

Under 2500 RPMs 3 and 4 aren't used. Only used above. Your problem is above...........

I "unknowingly" question how the PO checked the large filter and "betcha" didn't know or didn't bother with the small one for 3 and 4........which uses the large one too since is has a small amount of fuel mix added to the cylinders for lubrication, but not enough at low RPMs for combustion.....
Getting access to the large filter or a fuel line down wind of it is a PIA and if you went through the trouble of getting it out so that you could blow through it you might as well change it......about 10 bucks. I just sold my 2002 115 2+2.
Click to expand...
Thanks. I will see if I can get a replacement for this filter also
 
bigblocksarefun

bigblocksarefun

Petty Officer 2nd Class
Joined
Jan 27, 2008
Messages
139
I had this same problem with the Mariner version of this engine. Turned out to be the ADBV at the tank suction point. The little check ball had literally semi-welded itself in place.
 
A

aidanmurphy

Petty Officer 2nd Class
Joined
Apr 2, 2022
Messages
113
Ended up sticking a 6 gallon aux tank with fresh non ethanol fuel to run and the boat ran better but still did not resolve the top end fall off. I had my wife pump the bulb as we were WOT and I feel like it did improve the symptom but it is hard to tell as it is such a minor bog to begin with. One thing that I did find is that the PO has installed the incorrect barb into the crankcase for the fuel pump pulse line and that the line seemed like it was loose (just zip tied). I also put a real hose clamp on it and got it tight. This also could have led to the improved performance this time out. When I look at the OEM part online, the diameter is about double of the one that is installed. What is on the boat is one of those barbs that taper down. Now in theory, would this would cause a weaker pulse resulting in a weaker pull from the fuel pump? I already ordered the correct pulse barb so fingers crossed.
 
Last edited:
You must log in or register to reply here.
Top